Denis O'Hare was in Budapest working on a movie (the upcoming "The Eagle of the Ninth" co-starring Channing Tatum and Donald Sutherland) when he got the call.

HBODenis O'Hare in 'True Blood.'

"I was standing in front of a cathedral when my agent called from New York, " O'Hare said. "I was like, 'Why are you calling me?' He said, 'How would you like to be king of the vampires in Mississippi in 'True Blood?'

"I'm a big fan of the show. I think because I was such a fan of it, I never pushed to get on it or imagined being on it. I didn't imagine myself fitting in there. As an actor watching another show, it seems perfect, and you can't imagine inserting yourself in any way. I didn't see myself in it at all."

When O'Hare learned more about the role -- he joins the HBO drama in its third season, which premieres Sunday at 8 p.m., as a 2,800-year-old vampire -- the casting began to make some sense.

"I thought, 'Oh, this is totally me, ' " said O'Hare, a Tony Award winner who has worked in dozens of films (including "Milk, " "Garden State" and "Charlie Wilson's War") and guest-starred on nearly as many TV dramas (including "CSI: Miami, " "The Good Wife" and "Brothers & Sisters").

The character he plays, Russell Edgington, "is someone with a massive breadth of history, " O'Hare said. "He is at once savage and cultured. I think he's got a lot of charm and a lot of humor and he's deadly. Except for the deadly part, it's just like me."

A lot of actors are perfectly comfortable absorbing all the information they need for their character from the scripts that are written for them.

Not so with O'Hare, who did deep personal research on his charming, funny, deadly guy.

"One thing we decided early on is that he's clearly not from Mississippi, " he said, during a recent telephone interview from Los Angeles, where the series is mostly shot. "He was probably from East of the Danube, where the Celts came from. This guy moves across Europe through the sweep of history.

"We decided his base accent was something Germanic, so when the character gets exorcised or totally out of his mind, he slips into German.

"His move to Mississippi probably came during the rum trade.

"He assimilated. Vampires were illegal at that point (and) he had to meld himself into this culture."

O'Hare's research also extended to a road trip through Edgington's turf. He visited Jackson and Natchez (the Longwood Plantation there serves as the exterior of his character's home) and also took a swing through New Orleans.

"Basically it was an excuse to be in New Orleans, " he said. "In Mississippi there was this incredibly thick fog that rolls in in the morning and sticks around. For a vampire, that's like cheating. You get to be outside a little longer. You get to hang out. The sun can't quite penetrate."

O'Hare also did a lot of thinking about what it means to be very, very old -- and not look a day over 48.

"The first thing you encounter in your imagination is the notion that these people outlive their human contemporaries, " he said. "So the kind of contempt for humanity (Edgington displays) isn't born out of something based on the individual. It's based on the idea that these people don't exist for very long, so why would you form a relationship with them? They're just not worth it."

Another question: What does living to be 2,800 "do to your sense of discovery, your sense of adventure, your sense of appetite?" said O'Hare, whose character has had the same romantic partner (also a vampire, of course) for 700 years.

"Sexual fidelity after 700 years is just not going to happen, " he continued. "I'm sorry, it's just not possible. We've tried everything. But the fact that we've been together for 700 years means that loyalty goes beyond a sexual bond."

Sounds difficult. Also sounds like fun (for an actor).

"It's a total riot, " O'Hare said. "As an actor, the best playground is the imagination. You sit there in a scene and let your imagination go wild."